Plasma arc torch systems are widely used in the cutting of metallic materials. Such systems include a plasma arc torch mounted to a torch receptacle, an electrode mounted within the torch, a nozzle with a central exit orifice, electrical connections, passages for cooling and arc control fluids, a swirl ring to control the fluid flow patterns, and a power supply. The torch produces a plasma arc, which is a constricted ionized jet of a plasma gas with high temperature and high momentum. Gases used in the torch may be non-reactive, e.g. nitrogen or argon, or reactive, e.g. oxygen or air.
In process of plasma arc cutting of a metallic workpiece, a pilot arc potential (voltage) is first applied between the electrode (cathode) and the nozzle (anode). A voltage generated by a high voltage generator (HFHV) is applied to breakdown the gap between the electrode and the nozzle, allowing a pilot arc to form between the electrode and the nozzle. After the pilot arc is formed, the power supply initiates the transfer of the arc to the workpiece. The torch is operated in this transferred plasma arc mode, characterized by the conductive flow of ionized gas from the electrode to the workpiece, for the cutting of the workpiece.
Plasma arc cutting torches produce a transferred plasma jet with a current density that is typically in the range of 20,000 to 40,000 amperes/in.sup.2. High definition torches are characterized by narrower jets with higher current densities, typically about 60,000 amperes/in.sup.2. High definition torches produce a narrow cut kerf and a square cut angle. Such torches also have a thinner heat affected zone and are more effective in producing a dross free cut and blowing away molten metal.
In operation, high definition torches generally require efficient cooling of the nozzle. Liquid cooling has proven effective in achieving the required degree of cooling. In various high definition plasma arc torch systems manufactured by Hypertherm, Inc., a cooling liquid, such as water, circulates through the torch via internal passages and chambers, eventually flowing over portions of the nozzle to cool the nozzle.
Various problems have been found to exist in connection with the operation of plasma arc cutting torch systems. For example, when various consumable parts (e.g., the nozzle and electrode) require replacement, the torch is manually dissembled in a piece by piece manner. More specifically, the torch is disassembled to remove and replace worn consumables. Such changing processes require extensive human involvement and therefore may be time consuming and expensive.
It is therefore a principal object of this invention to provide a plasma arc cutting torch system that facilitates the changing of a torch.
Another principal object of this invention to provide a plasma arc cutting torch system that minimizes the amount of liquid leakage during the process of removing a torch.
Another principal object of this invention is to provide a cooling system for a plasma arc cutting torch that provides efficient and reliable cooling when the torch is started.